Mr Carmody's inquiry into the allegations operate under terms of reference that ask him to "review the adequacy and appropriateness of any response of, and action taken by, government to allegations, including allegations of criminal conduct associated with government responses, into historic child sexual abuse in youth detention centres."

Mr Carmody in his letter to Mr Bleijie on March 18, asked to widen the terms of reference because some people represented at the inquiry believed the current terms prevented him from investigating if he did not find evidence of "historic sex abuse".

"The practical effect of this, so those parties say, is to prevent me from continuing to hear evidence, or make findings about related facts or circumstances, unless I am able to confidently conclude that there was "historic child sexual abuse".

The inquiry has heard conflicting evidence on this specific subject.

Mr Carmody says in his letter to Mr Bleijie "I am yet to form a definitive view or make a decisive ruling on these submissions".

The commission of inquiry has heard evidence from 135 witnesses and seen 348 exhibits during this part of the inquiry.

Mr Carmody says in his letter that widening his terms of reference would not increase the cost or duration of his inquiry.

A spokesman for Mr Bleijie said the attorney-general received Mr Carmody's letter on Monday and it was now under "active consideration."